1. Field of the Invention
This invention relates to an injection molding machine comprising an injecting unit defining a horizontal injection axis and comprising a plasticizing cylinder centered on an movable along the injection axis. The injecting unit is mounted to be movable in a horizontal shifting direction transversely to the injection axis to a plurality of injecting positions and adapted in these injecting positions to selectively discharge plastic material out of the plasticizing cylinder along the injection axis on a plurality of parallel paths into central gatings of first injection molds and off-center gatings of further injection molds. In this way, a stationary mold carrier is provided with an enlarged opening in a shifting direction for receiving the plasticizing cylinder, which is moved by at least one drive unit along the injection axis into and out of engagement with any of the injection molds, when one of them is mounted on the mold carrier for the injection of synthetic material into the above mentioned gating. The stationary mold carrier is adapted to selectively carry the first and further injection molds. Guiding elements for ending sections of the drive unit extend up to the stationary mold carrier and are guided in the shifting direction when displacing the injection molding unit.
2. Description of the Prior Art
An injection molding machine of this kind is known from U.S. Pat. No. 5,007,816. This machine is adapted to selectively use further injection molds having off-center gatings in different injecting positions defining a central mold cavity. Under these conditions the plasticized synthetic material once injected reaches the mold cavity via a gate running approximately parallel with respect to the closing direction of the mold closing unit, which gate ends at the border of the mold cavity. A gate system of this kind in the following description is referred to as "parallel gating". In this machine the piston rods lying in a horizontal plane are movably guided. The injection molding unit is bedded on a carrier made of cast iron, which bears the injection molding unit and is shiftable on horizontal guidings to central and off-centered gatings. The shifting movement is realized by a shifting device operable by program, which comprises a distance measuring system as well as a spindle driving system. The shifting device is detachably fixed at the carrier. This arrangement allows a precise support and adjustment of the injection molding unit, whereby it is consciously accepted that costly supporting measures, in this case a shifting table, have to be provided. A further problem in this connection is that the feed screw is not easily accessible, especially for cleaning purposes, due to the preset arrangement of the injection molding unit parallely with respect to the injection axis. Because of the big distance between the shifting device and guiding elements, the danger of jams and inexact work is high.
Further, it is known from Swiss Patent 381,420 to arrange an injection molding unit transversely shiftable by a carrier on guiding elements fixedly connected to a machine base. The carrier itself abuts a further shifting device for horizontally moving the injection molding unit on further guidings to gates of injection molds. The guiding elements are angular guidings to enable an exact adjustment of the injection molding unit. Because of the loose connection between the mold carrier and injection molding unit, the injecting point of the nozzle differs from one injection cycle to the other and jams occur at the guiding elements for transversely moving the injection molding unit.
German Patent 40 34 577 discloses guiding piston rods of drive cylinders in a bushing support, which is passively carried along when the injection molding unit is shifted or also can be displaced manually. When the synthetic material is injected, a force in the piston rods opposed to the bearing pressure of the plasticizing cylinder has the effect that the bushing support is locked at punctiform guiding elements. Certainly it is a simple way to solve the connection of the bushings receiving the piston rods from the bushing support to the mold carrier, however, a field of force in the mold carrier results from the distance between the straining point of the piston rods and the force introducing points of the guiding elements, which makes necessary a lateral displacement of said guiding elements if shiftings of a large extent are to be realized. Consequently this facility is not adapted for an automatized shifting over the whole breadth of the mold carrier.